chapter 8.pdf

Photograph courtesy THA

Photograph courtesy THA

Photograph courtesy Tyrone Gopaul

Photograph courtesy Richard Edwards

CHAPTER 8

WATER RESOURCES

8 Water Resources Introduction Water is vital to all forms of life on earth,

from the simplest of living organisms to

the most complex of human systems. It

is a vital element in the social and

economic infrastructure and as

populations increase, the demand for

water grows. The health and welfare of

this increasing population bears a direct

relationship to the availability of water,

first for personal use and secondly for

use in their economic activities. Water

consumption is directly related to the

size, distribution and composition of the

population. Population projections

therefore assume major importance in

estimating future potable water

requirements. The main water-related

socio-economic activities in Trinidad and

Tobago are industry, agriculture,

recreation and tourism.

Leisure activity near The Creek in South Trinidad

Water requirement criteria set by the World Bank states that the minimum water

availability required to sustain human life is approximately 1000 cubic meters per capita

per year. Trinidad and Tobago, with an annual average water production of 2500 cubic

meters per capita per year, is clearly not a water scarce country. This availability

indicates that the water needs of the populace can be adequately met.

However, there is the potential for an increase in extreme events, for example, an

increase in flooding and or extended drought-like periods as a result of climate change.

The predicted impacts of global warming on these aspects are negative.

180

8.1 Water Production and Consumption

Potable water was first produced in Trinidad in 1835 with the commissioning of the Maraval

Water Treatment Plant, which had an output of 1 million gallons per day (mgd) whereas in

Tobago, Water Development started in 1952 with the commissioning of the Hillsborough Water

Treatment Facility, with a production of 1.5 mgd.

In Trinidad the total water production for the public water supply system increased steadily over

the period 1950 to 2002. In 1962, the Navet Waterworks and Treatment Plant were

commissioned to treat approximately 10 million cubic meters (10 MCM) per year. During the

period 1970 to 1990 the average supply increased by about 160 % from approximately 99 MCM

to 255 MCM per year.

Prior to the year 2000, surface water abstraction in Tobago accounted for approximately 98% of

the public water supply, with groundwater abstraction occurring primarily at Bloody Bay and

Government Farm in Scarborough. The public water supply was provided by the Hillsborough

impounding reservoir, two (2) intakes and three (3) wells to supply Scarborough and the West of

the island, while isolated intakes supplied the rest of the island on a local basis. Production data

for Trinidad for the period 1920 to 2004 and Tobago for the period 1971-2004 are presented in

Figures 8.1 and 8.2 respectively.

181

FIGURE 8.1 ANNUAL WATER PRODUCTION IN TRINIDAD, 1920 2004

0.00

50.00100.00

150.00200.00

250.00

300.00350.00

400.0019

20

1930

1940

1950

1960

1970

1972

1974

1976

1978

1980

1982

1984

1986

1988

1990

1992

1994

1996

1998

2000

2002

2004

Year

Pro

duct

ion

(106

m3 )

Throughout the mid to late 1990s various programmes aimed at augmenting the public water

supply have been commissioned. These developments include the South and North Water

projects (1998-2000), the Caroni Water Treatment Plant upgrade (1999), the Tobago Well

Development (2000), and The Trinidad Well Development Programme.

182

FIGURE 8.2 ANNUAL WATER PRODUCTION IN TOBAGO, 1971 2004

0

2

4

6

8

10

12

1419

71

1973

1975

1977

1979

1981

1983

1985

1987

1989

1991

1993

1995

1997

1999

2001

2003

Year

Prod

uctio

n ( 1

06 m

3 )

Source of Figs 8.1 and 8.2: Water and Sewerage Authority of Trinidad and Tobago

During the year 2001, total water production in Trinidad and Tobago stood at approximately 291

MCM per year. Approximately 207 MCM (71%) came from surface water sources, while

groundwater production accounted for the balance of 84 MCM (29 %).

8.2 Existing State of the Water Supply Sector Throughout the decades, the expansion and improvements in the public water supply network

has continued to such an extent that today outlying districts in, for example, Cedros and Moruga

are connected to the distribution system. It is estimated that at present approximately 86% of

the population of Trinidad and Tobago has a potable water supply. This is expected to increase

to 98% by the year 2010.

183

The public water supply is composed of both surface and groundwater sources. The various

components of public water supply system for both islands are presented in Table 8.1. A

cursory glance at these tables reveals that, with the exception of the Navet scheme, the major

portion of the surface water input into WASAs production capacity in Trinidad is obtained from

river intakes and storage dams in the Northern areas of the country. It is essential to recognize

that the sustainability of the countrys water supplies depends on maintaining these surface

water systems.

TABLE 8.1 THE PUBLIC WATER SUPPLY SYSTEM OF TRINIDAD AND TOBAGO

System Components

Northern Systems Hollis Reservoir and other smaller intakes serves Arima and surroundings

North Oropuche River Intake to serve Sangre Grande, Arima and Westwards.

Caroni Dam and WTP A major reservoir in the North Central to serve the North and South of the island in an approximate 50:50 ratio.

NorthWest System Water from Caroni North is supplemented by seven (7) wellfields and river intakes to serve the City of Port-of-Spain and suburbs.

Southern System Water from Caroni South for areas in Central (including Point Lisas) and South.

Navet Scheme The second largest reservoir in the Central area to serve the City of San Fernando and suburbs.

Isolated South Plants Small intakes, and wellfield within the South one-third of the island to supply localised demands.

Tobago South west System

Hillsborough impounding reservoir, two (2) intakes and eight (8) wells to supply Scarborough and the West of the island.

Tobago - Isolated Plants Three (3) small intakes and four (4) wells supply the rest of the island on a localised basis.

Source: Water and Sewerage Authority of Trinidad and Tobago

184

TABLE 8.2 IMPORTANT FACTS ON WATER RESOURCES IN TRINIDAD AND TOBAGO

Number of Water Production Sources 142 Pumping stations (booster station) 110 Rural intakes and spring sources 48 Wells 439 Surface reservoirs with a total capacity of 409 millions gallon (85 in use)

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Water treatment plants 57 Lift stations 24 Water customers 300,000 Wastewater customers 46,000 Raw water reservoirs: Arena Hollis Navet Hillsborough

9.8 billion gallons capacity 1.04 billion gallons capacity 4.1 billion gallons capacity 225 million gallons capacity

Water mains (pipeline) ranging from 20 mm to 1,350mm in diameter

4,073.7 kilometers

Public sewer mains 1,140km Population- access to water services 90% Population- covered by WASA wastewater 20% 24/7 supply of water 18% Compliance- chemical 63% Wastewater water treated 200 i.m.g.d.


Hillsborough Dam in Tobago Navet Dam - Trinidad

185

Arena Dam - Trinidad Hollis Dam Trinidad

8.3 Water Demand

The demand for water on the islands is classified as consuming or non-consuming. The former

includes domestic water, industrial (major and minor), irrigation requirements and unaccounted-

for-water (UFW). The latter classification is related to the minimum flows required to maintain

healthy ecosystems in rivers and swamps, and is generally estimated as a minimum of 20% of

the natural river flow.

Estimates of consuming demands for the year 1997 and future projections in Trinidad and

Tobago are shown in Figures 8.3 and 8.4. The proportion of each demand component with

respect to the overall demand in 2000 is illustrated in Figures 8.5 and 8.6

While there is no formal policy, allocation of the resources among competing users is in the

following order of priority: - domestic, industrial, agricultural and ecological. However, there are

many cases where the order of priority changes within certain basins.

186

FIGURE 8.3 CONSUMING WATER DEMAND FOR TRINIDAD, 1997 2025

0

50

100

150

200

250

1997

2000

2005

2015

2025

Year

Dem

and

(MC

M)

Domestic Maj ind Min ind Agriculture U.F.W.


The water demand for domestic consumers

was calculated using a population growth

rate of 0 .7 % per annum, beginning with a

population base of 1.3 million in 1995 and a

per capita consumption of 2 cubic meters

m3/day. Estimated UWF was 43% for 1997,

and expected to decline to 30% in the 2025.

FIGURE 8.4 CONSUMING WATER DEMAND FOR TOBAGO, 1997 2025

012

345678

1997

2000

2005

2015

2025

Year

Dem

and

(MC

M)

Dom estic M aj ind M in ind Agriculture U.F .W .


187

Irrigation demand estimates have been obtained by scrutiny of the irrigated area (present base-

3, 40 hectares), the unit demand for each crop, and irrigation efficiency. Given the current

economic outlook, indications are that this sector will not expand significantly over the period. However, there are substantial amounts of arable lands, which, when irrigated, could provide for

expansion in the agricultural sector. Unlikely though that is, should that happen the demand for

irrigation water will increase dramatically, and will have to be factored in the projections.

FIGURE 8.5 PROPORTIONS OF COMPETING CONSUMING DEMANDS,

Trinidad 2000


2.54 MCM34%

4.7 MCM64%

0.16 M

CM 2%

Domestic

Maj ind

Min ind

Agriculture

U.F.W.

FIGURE 8.6 PROPORTIONS OF COMPETING CONSUMING DEMANDS, Tobago 2000 Source: Water and Sewerage Authority of Trinidad and Tobago

10 M

CM

3%

124 MCM41%

116 MCM37%

51 MCM16%

10 M

CM 3

%

DomesticMaj indMin indAgricultureU.F.W.

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8.4 Public Water Supply and Demand In 1997, the demand was generally equaled

by water production in Trinidad. In 2000,

WASA reported that 288 MCM of water was

produced from surface water and

groundwater sources for the public water

system in Trinidad. During this year

however, a total non-consuming water

demand of 311 MCM was reported, leading

to a deficit of some 23 MCM.

Similarly in Tobago, water production

generally satisfied demand in 1997. In 2000,

WASA reported that 12 MCM was supplied

to its customers through the public water

system. During this year, a total non-

consuming water demand of 8.7 MCM was

reported. Approximately 4 MCM of this

supply originated from recently developed

groundwater sources in bedrock aquifers.

The public water supply and demand

situation for the islands is presented in

Figures 8.7 and 8.8.

WASA pipeline

189

FIGURE 8.7 PUBLIC WATER SUPPLY AND DEMAND IN TRINIDAD, 1997 AND 2000

19972000

Dem and

Production

282 288

279

311

260

270

280

290

300

310

320

Qua

ntity

(MC

M)


Figure 8.7 shows a shortfall in the

production supply in the year 2000.

However, it must be realized that these

demand and production figures are

averages over the country and over

individual year periods. It must also be

remembered that:

They do not reflect daily variations where these are not buffered by storage They do not reflect seasonal variations The supply-versus-demand situation varies from area to area in the country

(distribution restrictions)

The supply is presently intermittent in many areas and therefore where a twenty-four hour supply is contemplated, losses may well be considerably higher than the

assumed 34%.

Furthermore, the reliability of the production data may be limited by the distribution of

functioning metering devices. Production records in many cases are likely to reflect only the

number of days or months that the facility has been operational at a production rate, which is

presumed to equate to the original design capacity.

190

FIGURE 8.8 PUBLIC WATER SUPPLY AND DEMAND IN TOBAGO, 1997 and 2000

19972000

Demand

Production

10.0

12.0

8.8 8.7

0

2

4

6

8

10

12

14

Qua

ntity

(MC

M)


Therefore, considering the actual situation in Trinidad and Tobago where scheduled supply is

judged necessary in many areas in order to distribute inadequate resources as best as possible,

it must be concluded that:

Maximum effort must be made to reduce leakage Improvements must be made to the distribution system to bring water from the

production facilities to the demand areas

Existing production facilities must be refurbished so as to ensure maximum output Additional production facilities should be planned, designed and constructed Data collection on actual supply and demand must be improved.

191

8.5 Industrial Demand and Sea Water Desalination

Projected scenarios indicate that the demand for domestic water is expected to nearly double

over the next twenty-five (25) years while the industrial demand will increase by three (3) times

over the same period.

To meet short term industrial demand at Point Lisas, a new source of water had to be

developed as soon as possible. It was evident from the recent rapid growth in industrial

demand, that there was need for a short-term, low-risk solution. After an exhaustive look at all

available alternatives, an on-site desalination plant was recommended (WRMS, 1999). The

plant was subsequently commissioned in March 2002.

Based on the projected growth in demand of the industrial, domestic, agricultural/irrigation and

tourism sectors, from a national supply point of view the desalination plant is only a temporary

measure. The provision of a desalination plant at Point Lisas was recommended as being the

most important part in a plan stressing the need to relieve the burden on the domestic water

supply system in the shortest possible time. The development of intakes and reservoir systems

in areas such as North Oropouche, Matura, and Moruga have proved the most reliable supply,

but due to their lengthy gestation period of between ten (10) and fifteen (15) years are not

expected to be completed before 2015.

The desalination project has provided short-term relief, by reducing the gap between water

demand and supply in the estate. The deslination plant has reduced current shortfall and allows

more water from Caroni Waterworks to be available to improve supplies to domestic customers.

Although seawater desalination is new to Trinidad, it is an option adopted for the provision of

potable water by many countries of the world including Barbados here in the Caribbean. The

advantages of this project are a limitless supply of seawater from the Gulf of Paria and the

lessening of transmission losses due to the close proximity of the demand centre.

The Point Lisas desalination facility is owned and operated by the Desalination Company of

Trinidad and Tobago (Desalcott). WASA purchased 25.86 MCM from the plant in 2002 and

35.08 MCM in 2003.

192

8.6 Watersheds and Catchments StatusFor the purposes of watershed management, Trinidad and Tobago has been subdivided into

fifty-four (54) and fifteen (15) watershed areas respectively, as illustrated in Map 8.1. By

reducing catchment degradation and soil erosion rates, watershed management practices aim

to have a significant effect on the countrys water resources.

193

MAP 8.1 CATCHMENT AREAS OF TRINIDAD AND TOBAGO


The timing and distribution of the streamflow within the catchment, and the sediment load of

discharges entering the lower reaches of rivers are particularly influenced by the state of a

particular watershed. Proper watershed management practices strive to minimise the sediment

load in river systems, thereby reducing reservoir storage losses, treatment costs and incidents

of flooding.

194

8.7 Water Pollution

Categories of Pollution

Surface Water Systems:

The major pollutants found in the Trinidad and Tobago water systems are solids (measured as

total suspended solids), organics (measured as biological oxygen demand), oil and grease,

nitrogen and phosphorous. The relative percentages of these pollutant loads and their sources

are shown in Figure 8.8. Other pollutants, heavy metals namely nickel, cadmium, chromium,

lead, zinc and copper were also detected in certain river systems and river sediments across

Trinidad and Tobago. However, only lead, zinc and copper were above the United States

Environment Protection Agency (USEPA) National Recommended Water Quality Criteria

(Corrected, 1999).

Water turbidity of water course in South Trinidad

195

FIGURE 8.9 MAJOR POLLUTANTS IN TRINIDAD AND TOBAGOS WATER SYSTEMS, 1998

livestock rearing, municipal w aste

treatment, manufacturing of beverages and petrochemicals,

petroleum refining and hospitality

18%

municipal w aste treatment, livestock rearing, beverage manufacturing and

petreoleum refininged Solids37%

municipal w aste treatment and livestock

rearings1%

municipal w aste treatment, livestock

rearing and manufacturing of petrochemicals

9%

oil and fatsproduction, petroleum refining,

petrochemical manufacturing and municipal w aste

treatment35%

BiologicalOxygen Demand

Total SuspendedSolidsNitrogen

Phosphorous

Oil & Grease

Source: Environmental Management Authority, 1998

Trinidad and Tobago is one of the most industrialised countries in the Caribbean region with

industries ranging from sugar and oil refining, rum distillation and the manufacture of petro-

chemicals, to paint, metal finishing, and agro-processing. Effluents from oil and sugar cane

refining affect the rivers in South Trinidad. The impact of industrial effluents on water resources

is seen mainly along the foothills of the Northern Range, Central-West and the South-West

coast of Trinidad. Industrial activity in Tobago is relatively small, being concentrated in the

South-West and Central parts of the island.

Most of the sewerage treatment plants operating in Trinidad and Tobago are inefficient, since

they produce effluent, which exceeds the standards for faecal coliform and biological oxygen

demand (BOD). Non-functional sewerage treatment plants, livestock farms, overflowing septic

tanks and pit latrines discharge significant quantities of organic waste into the nations

waterways.

The total domestic and livestock waste for Trinidad and Tobago was estimated as 10.4 million

kilograms/year with 45% being contributed from domestic sources and 55% from livestock.

Table 8.3 shows the annual pollutant loads for BOD, suspended solids, nitrogen and

196

phosphorous. It must be noted that Tobago accounts for 4% of both the domestic waste and

livestock waste.

TABLE 8.3 WASTE LOAD PRODUCTION/DISCHARGES FOR TRINIDAD AND TOBAGO

BOD Suspended Solids Nitrogen PhosphorousCountry Source Type of Load (x 1000 kg/yr) (x1000 kg/yr) (x 1000 kg/yr) (x 1000 kg/yr)

Domestic Produced 19,371 114,073 3,300 825Trinidad Livestock Produced 39,444 105,980 3,460 562

Domestic Discharged 1,438 2,593 492 131Tobago Livestock Discharged 197 5,299 173 28


Substantial quantities of domestic refuse and solid wastes are dumped in the watercourses of

Trinidad and Tobago. These wastes consist of animal entrails, chicken feathers, faeces, used

containers, and bulky household items. Domestic refuse and solid waste not only clog the

waterways and produce offensive odours, but may also dissolve to produce chemical residues

which lower water quality.

The existing wastewater infrastructure covers only thirty percent (30%) of the population, with

WASA covering twenty percent (20%) of this figure and other providers the remaining ten (10%)

percent. The remainder of the population is covered by either private on lot systems such as

cesspits and soakaways or pit latrines.

The total volume of wastewater treated is approximately 200 i.m.g.d. There are over 200

Wastewater Treatment Plants (WWTPs) of which 35 are either WASA owned or operated.

Twelve (12) were originally owned by WASA while twenty-one (23) plants have been taken over

from the HDC (previously NHA), one (1) from the LSA and one (1) from the Sugar & Welfare.

Some of the major WWTPs in Trinidad and Tobago are:

197

New Beetham WWTP

San Fernando WWTP

Arima WWTP

Scarborough WWWTP

Trincity WWTP

Penco Lands WWTP

Lange Park WWTP

Malabar WWTP

Techier WWTP

Edinburgh WWTP

Point Gourde WWTP

The Authority has embarked on the implementation of some of the recommendations of several

studies conducted on the wastewater sector in Trinidad and Tobago, including:

Construction of a new wastewater treatment plant at Beetham to serve three hundred and sixty thousand customers of the greater Port of Spain area (nearing completion);

Construction of a wastewater facility for Southwest Tobago; Adoption/regularization, on a phased-basis, of all NHA and private package wastewater

treatment plants

The Water and Sewerage Authority (WASA) conducts the most extensive ongoing water quality

monitoring in the country through its routine samplings at all surface water intakes. The sampling

regime, although focused on water sources for the public water supply, yields information

characteristic of a substantial portion of the island of Trinidad. Over the years there is proof that

many surface bodies of water are affected by high levels of organic material (expressed as BOD),

pathogens (expressed as faecal coliform) and solids (expressed as turbidity). Table 8.4 shows data

from this sample regime for the year 1995.

This table shows clearly that most rivers are heavily polluted, the only exception being the North

Oropouche River while the South Oropouche River still has a reasonable water quality. There is

very little difference between the main Caroni River and its tributaries. All suffer from

uncontrolled waste discharges and the poor performance of wastewater treatment plants,

resulting in high BOD loads and low dissolved oxygen contents. This is also the case in the

Couva, Guaracara and Cipero Rivers. The Cipero River shows particularly excessive BOD

levels. The high BOD figure for the Couva River is due to one sampling point downstream of a

major ammonia based fertilizer plant.

198

TABLE 8.4 AVERAGES PER RIVER OF THE MEAN 1995 CONCENTRATIONS FOR WASA SAMPLING AREAS

Substances BOD Ortho Phos-phate

Total P DO FC

Free N

Settle-able

Matter Total NFR

River mg/l mg/l mg/l mg/l nr/100ml mg/l mg/l mg/l

North Oropouche 0.90 0.04 0.19 7.40 770 0.20 0.02 25

Caroni (main) 9.80 0.24 0.55 4.50 122,885 0.90 0.14 29

Caroni (trib.) 10.50 0.27 0.57 4.90 144,850 0.90 0.16 17

Couva 23.00 0.07 0.34 6.40 15,120 1.90 0.44 145

Guaracara 15.00 0.08 0.35 4.70 25,350 1.60 0.30 69

Cipero 342.5 0.17 0.50 3.10 171,213 1.50 0.94 66

South Oropouche 3.90 0.05 0.37 5.50 16,387 0.50 0.06 225Average all locations 58.10 0.16 0.46 4.90 88,486 1.00 0.27 78


BOD - Biological Oxygen Demand P - Phosphorous DO- Dissolved Oxygen Concentration FC - Faecal Coliform NFR - Non-Filtration Residue

Two (2) major water quality studies (1977 and 1999) in the country have been restricted to the

Caroni River Basin, the major water-producing basin in the country, where the Caroni Water

Treatment Plant producing 40% of Trinidads water supply is located. The Caroni River is one

of the major rivers in Trinidad, with a length of approximately 35 km, from its source to the

mouth in the Gulf of Paria; it receives water from fourteen (14) tributary streams. There are two

main industrialized areas along the Caroni River. However, for most of its length the Caroni

River flows through sugar cane fields with scattered settlements.

Monitoring of the Caroni River and its tributaries during the wet season (1999) showed a

progressive increase in pollutant levels from the upper Caroni River, mid Caroni River and lower

Caroni River. There were increases in levels of ammonia, BOD5, chlorides, nitrates,

phosphates, total and faecal coliforms. Consistently low dissolved oxygen levels and high BOD

and faecal coliforms indicated considerable organic pollution in the Caroni River. Elevated levels

of hydrogen sulphide and the foul smell of this gas were consistent with the anoxic condition of

the Caroni River. Continued monitoring of the Caroni River during the dry season showed a

similar trend to that of the wet season. There were progressive increases downstream in BOD5,

199

nutrients, total and faecal coliforms with consistent lowering in dissolved oxygen. The anoxic

condition of the Caroni River, due to extensive pollution, makes the water quality extremely

poor.

The origins of the individual pollutants were identified as follows:

Nitrogen (ammonia) Mainly from the flushing of soil constituents

Nitrogen (nitrates) Mainly from point source (municipal and industrial) discharges.

Soil constituents may also be a minor source

Nitrogen (nitrites) Mainly from point sources and soil constraints

BOD

Oil and Grease

Total Phosphorous

Solids Mainly from particulate matter derived from Sheet erosion, bed

mobilization and the flushing of soil constituents

The majority of the rivers in the study area were found to be polluted with industrial and

domestic wastes and includes agricultural wastes proceeding from poor land use practices.

Field surveillance studies in the watersheds of the Caroni River Basin identified the major

activities affecting the catchments as quarrying, industrial and domestic waste discharges, and

domestic dumping of solid waste.

The water quality problems were attributed to:

Untreated effluent discharges by households and industry

Limited waste water treatment capacity

200

Low efficiency of existing waste water treatment facilities

Lack of sewer systems and only a small fraction (40%) of households connected to

available sewers

Surface runoff (turbidity)

There have been several incidences of spills on land in the Southern one-third of the island that

have resulted in severe pollution of the waterways in these areas. These spills often drain into

coastal areas causing substantial damage to the mangrove and beach. The South-East and

South-West areas are those most often affected. Recent efforts by the Ministry of Energy to limit

such damage through the enforcement of clean-up actions by the polluters have had some,

albeit limited, success to date.

Chronic oil pollution is not as severe a problem. However, the chronic discharge of oilfield brines

from producing wells has changed the salinity of several small waterways and thus their natural

environment. The impact of this form of pollution on coastal zones is considered minimal. While

there is no comprehensive island-wide assessment of the quality of the water resources of the

country, a number of independent studies of varying levels of reliability have been carried out.

Consequently the results of these studies, together with expert opinion, and the results of the

Caroni River Basin water quality studies, have been combined to arrive at an overview of the

quality of the surface water resource of Trinidad and Tobago. The overview shows a relatively

low surface water quality in the North, Central and Western part of Trinidad, while the North-

eastern part of Trinidad and Tobago has relatively high water quality levels. The activities

affecting the water quality and the aquatic environment are (watershed degradation)

modification of the hydrological regime, discharge of chemicals, disposal of sewerage and farm

wastes, and the dumping of refuse and solid wastes.

8.8 Heavy Metal and Physico-chemical Pollution In a study carried out by the University of the West Indies: Life Sciences and Chemistry

Departments which was presented at the Commonwealth Environmental Health Institute (CEHI)

Conference in 2004, it was found that heavy metals such as lead, zinc and copper were indeed

present in the rivers of Trinidad and Tobago as well as in the river sediments themselves. The

study was carried out at sixty-four (64) sites across Trinidad and Tobago from November 1998

201

to June 2001 and the rivers were judged in three (3) categories: clean (free from heavy metal

and physico-chemical pollution), perturbed (slightly contaminated with heavy metals but still

useable) and polluted (well contaminated and not useable).

The following Map 8.2 shows the variation of the physico-chemical pollution across Trinidad. It

can be seen that most of the rivers monitored across the North, Central and East were clean.

However, in the areas of Central, and most of South were either polluted or perturbed.

MAP 8.2 PHYSICO-CHEMICAL SURFACE WATER QUALITY

Source: University of the West Indies, 2001 Source: University of the West Indies, 2001 a. Watersheds and Intakes b. Land Use

West Peninsula/Caroni Nariva Agriculture

Commercial/Industr./Residential Central West Swamp/Reservoirs North Coast Grasslands North Oropouche Forest

Cedros Peninsula South Oropouche Southern Range Ortoire Disturbed natural ecosystem

Pitch Lake

202

Map 8.3 shows the analysis of the heavy metal pollution of river waters in Trinidad. Only a small

number of rivers (one on the North coast and five spread across the North and central regions)

can be categorized as clean.

MAP 8.3 HEAVY METALS IN THE SURFACE WATERS OF RIVERS OF TRINIDAD

a. Watersheds and Intakes b. Land Use

Source: University of the West Indies, 2001 Source: University of the West Indies, 2001

Water Intake or Extraction point

Clean Perturbed Polluted

Town

Roads

Disturbed natural ecosystem

Agriculture Commercial/Industrial/Residential Swamp/Reservoirs Grasslands Forest

Pitch Lake

West Peninsula/Caroni Nariva

Central West North Coast North Oropouche Ortoire Southern Range South Oropouche Cedros Peninsula

203

Heavy metals were also detected in

samples of sediments on the monitored

rivers, as sediments tend to trap the

presence of pollution for a longer period of

time. This analysis showed that there were

no clean rivers to be found across the

country. Rivers of the North Coast also

showed signs of heavy metal pollution.

However, this may be due to the geology of

the soils in that area. The North-West

Peninsula/ Caroni Region also showed most

of the sampled sediment as polluted with

few perturbed areas. The rest of Trinidad

showed mainly perturbed sediment with

some areas in South as polluted. The

following map illustrates this (see Map 8.4).

MAP 8.4 HEAVY METALS IN THE SEDIMENTS OF RIVERS OF TRINIDAD

a. Watersheds and Intakes b. Land Use

Source: University of the West Indies, 2001 Source: University of the West Indies, 2001

West Peninsula/Caroni Nariva Clean

Agriculture Perturbed Polluted Commercial/Industrial/Residential Central West

Swamp/Reservoirs North Coast Water Intake or Extraction point Grasslands North Oropouche

Cedros Peninsula South Southern Range Ortoire Forest

Disturbed natural ecosystem Town Pitch Lake Roads

204

TABLE 8.5 WATER QUALITY OF TOBAGO RIVERS

SITE UPPER /LOWER PHYSICO SEDIMENT WATER

1 Bloody Bay Perturbed Polluted Clean

2 Courland Upper Clean Perturbed Perturbed

3 Courland Lower Clean Perturbed Perturbed

4 Hillsborough West Lower N/A Polluted Perturbed

5 Lambeau Lower Perturbed Polluted Perturbed

6 Louis Dor Lower Clean Polluted Clean

7 Louis Dor Upper Clean Polluted Clean

8 Speyside Upper Clean Polluted Polluted

9 Speyside Lower Clean Polluted Perturbed Source: Water and Sewerage Authority of Trinidad and Tobago

N/A Not Applicable

8.9 Geochemistry of Surface Water

The natural surface waters of both islands

are fresh high quality potable water of low

dissolved solids (250 to 650 milligrams per

litre), low chlorides (

8.10 Groundwater Systems

On the whole, there have been no instances of significant widespread groundwater pollution in

Trinidad and Tobago. However, preliminary data indicated that there may be localised seepage

of hydrocarbons into the sub-surface environment in the vicinity of gas stations. Consequently a

comprehensive study was undertaken in Trinidad by the EMA in conjunction with National

Petroleum Marketing Company and the WRA. The report on this study indicates the presence of

MTBE (methyl tertiary butyl ether) and BTEX (benzene, toluene, ethylbenzene and xylene) in

areas of North Trinidad that are relatively close to gas stations. At present, there is no real

cause for concern with respect to MTBE and BTEX pollution in Tobago. However, mitigation

measures must be put in place to prevent such disasters in the future since gasoline storage

tanks are constantly deteriorating.

MTBE is a carcinogenic substance that is soluble in water and not easily absorbed into the soil

which means it can spread faster and farther in the ground than other gasoline chemicals.

MTBE does not biodegrade and will, therefore, persist in groundwater. BTEX is made up of all

components of gasoline. It is also very carcinogenic and its mere presence in groundwater

indicates the possibility of leaking gasoline storage tanks.

Excessive chloride concentrations (>250 mg/l) have been recorded in aquifers in close proximity

to the coast (e.g. Port-of-Spain Gravels, Diego Martin Gravels, El Socorro Gravels, Mayaro

Sandstone). This is due to localised seawater intrusion whenever over-abstraction occurs. In

Tobago, recent quality assessments (WASA, 2000) of the groundwater systems show that there

are no significant pollution concerns.

Given the state of pollution of Trinidads surface water systems, the lack of detection of

significant contamination in the islands aquifers is surprising. This may be related to the

frequency and method of groundwater quality monitoring being employed. The most advanced

methods to detect micro-pollutants such as polychlorinated biphenyls (PCBs), polyaromatic

hydrocarbons (PAHs), pesticides, and benezene, toluene, ethylbenzene and xzylene (BTEXs)

need to be employed on a more sustained basis.

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The threats to groundwater quality appear to be by point source pollution, occurring on a

local scale. In the absence of thick overlaying clay layers, some aquifer systems are

vulnerable to infiltration by contaminants. The potential risk of pollution to aquifers may

be the result of leakage from:

Hazardous waste dump;

Underground fuel storage tanks;

Untreated sewerage;

Industrial activities;

Pit latrines and septic tanks

8.11 Geochemistry of Groundwater Groundwater varies in composition throughout the various sources in the islands. In Trinidad the

North-West Peninsula Gravels are of mediocre hardness and little iron. Elevated levels of

chloride and hardness are present in one coastal aquifer that experienced salt-water intrusion.

Within the Northern Gravels the El Socorro aquifer has also been over-pumped resulting in

elevated levels of salinity and hardness. The other aquifers are generally fresher and higher in

iron as one travels from West to East.

TABLE 8.6 NATURAL WATER QUALITY OF MAJOR GROUNDWATER SOURCES

Aquifer Systems TDS mg/L Chloride

mg/L Hardness

mg/L Alkalinity

mg/L Iron mg/L

NorthWest Gravels 125 128 18 33 75 200 42 180 0.00 0.08

Northern Gravels 122 420 20 100 28 200 15 200 0.00 0.14

Central Sands 75 430 10 140 15 120 120 250 0.10 7.25

Southern Sands 70 720 10 160 15 200 30 410 0.20 2.30 Source: Water and Sewerage Authority of Trinidad and Tobago

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The Central Sands are generally very fresh with the exception of Sum Sum aquifer in Carlsen

Field, the Mahaica Sands of Wallerfield and the Durham Sands of Freeport. Hardness and

alkalinity are also elevated in these aquifers contributing to the elevated Total Dissolved Solids

(TDS) levels; however, higher chlorides also contributed to the TDS levels of Carlsen Field.

Most of the Central Sand aquifers contain substantial iron, the exception being Sum Sum Sands

in Carlsen Field and Mahaica in Wallerfield.

The Southern Sands have high TDS values with the exception of the Erin Sands of Granville.

The high TDS values always correlate with high hardness and alkalinity (due to calcium and

magnesium carbonates). Iron levels are significant but not as high as in the Central Sands.

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